The Electrochemical Behaviour of Cadmium in Aqueous Solutions EIS Investigation

Abstract

Cadmium is occuring at the dividing line between noble and base metals. The metal has better corrosion resistance than zinc and a greater domain for immunity. The remarkable biological and environmental pollution caused by cadmium makes the corrosion behaviour of this metal important case worthy of intensive studies. The few investigations done on cadmium in the last decades were concerned with the mechanism of anodic dissolution of Cd and cathodic reduction of Cd 2+ in aqueous solutions. The proposed mechanism involves two consecutive charge transfer reactions. In the present investigation a systematic study of the electrochemical behaviour of Cd in aqueous solutions of different pH was carried out. Open-circuit potential measurements, polarization and electrochemical impedance spectroscopy (EIS) techniques were employed. The experimental results have shown that the corrosion behaviour of the metal in aqueous solutions is dependent on the solution pH. The presence of oxygen passivates the metal surface in neutral and basic solutions. In acidic solutions, on the other hand, no remarkable effect of oxygen was recorded. EIS data showed the presence of two phase maxima in neutral solutions which can be explained on the basis of the presence of two consecutive processes with two different time constants occurring at the electrode/ electrolyte interface. The mechanism of the corrosion and passivation processes occurring at the electrode/ electrolyte interface in different solutions was discussed. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) confirm the proposed mechanism.